Terrestrial radio broadcasting in North America is called HD radio and employs the in-band on-channel (IBOC) technology. According to the IBOC standard, analog and digital radio broadcast waves are transmitted. The analog radio broadcast waves are obtained by modulating audio signals with amplitude modulation (AM) or frequency modulation (FM). The digital radio broadcast waves are obtained by modulating audio signals with orthogonal frequency division multiplexing (OFDM) modulation. The IBOC standard requires transmitting the digital radio broadcast waves in frequency bands on both sides of a frequency band of the analog radio broadcast waves. Therefore, in the IBOC standard, a radio reception apparatus can receive the analog radio broadcast waves and the digital radio broadcast waves simultaneously by receiving radio waves on one frequency.
In the IBOC standard, the analog radio broadcast waves and the digital radio broadcast waves, which are transmitted in the same frequency band, include audio signals representing the same content. When the reception state is good, the radio reception apparatus can demodulate and output the audio signals of the digital radio broadcast waves. When the reception state is bad, the radio reception apparatus can demodulate and output the audio signals of the analog radio broadcast waves.
When the reception state changes from the bad state to the good state, the radio reception apparatus switch output signals from audio signals of the analog radio broadcast waves to audio signals of the digital radio broadcast waves. Thus, the radio reception apparatus can output the audio signals having appropriate quality corresponding to the reception state.
However, quality of the audio signals of the analog radio broadcast waves is significantly different from that of the audio signals of the digital radio broadcast waves. Consequently, quality of audio signals output by the radio reception apparatus suddenly becomes good at the timing of switching the output signals from the audio signals of the analog radio broadcast waves to those of the digital radio broadcast waves. This may give great aural discomfort to users.